AA is a very general concept and relates to visual of CGI (computer generated images) on raster (bitmap-based) displays. It means smoothing out the edges of rendered objects on screen according to one of several algorithms related to the domain of the problem. Usually it requires the ability to render the object in higher resolution than that of the display, and then "adapt" (usually subsample) the high resolution render to the low resolution display.
example:
AA of shapes (lines, circles, etc).
AA of text (in windows there's "plain" and "clear-type" which is suited for LCD)
AA of 3D scenes
Each of the above domains has different techniques and various methods to smooth out the look.
hope it's a good start